Hundreds of ATMs across India's tech hub remained shut for the second day due to possible virus attack by WannaCry ransomware and cash crunch, said a bank official on Tuesday.

"Ransomware attack appears to be causing glitches at many ATMs that work on Random Access Memory (RAM). Old ATMs are affected by the malware," State Bank of India Officers' Association Secretary General R. Ramesh said.

New Automatic Teller Machines (ATMs) with Microsoft's Windows 10, however, were not affected by the ransomware.

Cash crunch at treasury offices of state-run banks also forced the security staff to display 'No Cash' or 'Out of Order' signboards at their ATMs across the city and shut them from operating.

"My mother returned from an SBI ATM without drawing cash as it remained shut with 'No Cash' sign board on the machine," lamented S. Ramya, a college student.

Of the 18,000 ATMs across Karnataka, about 10,000 are in Bengaluru alone.

"Our engineers are trying to fix the problem so that ATMs could resume dispensing cash from Wednesday," said Mr Ramesh.

All-India Bank Officers Confederation Secretary S.K. Srinivas said the auto-shutdown of ATMs would be rectified soon.

"There is enough cash with the banks for withdrawals through the counters. Customers need not worry about their security of their money," reiterated Mr Srinivas.

Bank officials, however advised customers to avoid online transactions till further notice due to uncertainty over the impact of ransomware on internet banking.